During the 1970s and early 1980s, many farmers became conscious of the need to conserve their most valuable resource--namely, the soil itself. Farmers became aware that prior practices in deep tillage using moldboard plows were useful in that they loosened soil to depths of 6-8 inches, which promoted root growth, moisture retention and plant development, but this benefit occurred with a substantial loss of valuable topsoil through erosion.
Farmers began experimenting with practices referred to as "no-till" farming (in which crop residue is simply left on the top of the soil and there is, literally, no primary tillage of the soil) ridge-till farming, and other methods. Eventually, many of the practices and techniques evolved into a broad category of farming referred to as "conservation tillage". Individually practices may vary widely depending upon weather conditions, soil conditions, the nature of the crop, and many other factors. However, most farmers in the 1980s and 1990s began to practice at least some techniques for soil conservation, yet they found the need, as well, for at least some primary tillage.
It was in such circumstances that it became popular to use chisel plows with "no-till" or MRD (minimum residue displacement) shanks, as distinguished from conventional parabolic shanks, which create greater soil disruption and surface residue displacement. The arrangements, configurations and plow point structure employed vary widely.
In general, Minimum Soil Displacement (or MSD for short) chisel plow row units are mounted to a common frame or toolbar. The units are spaced transversely of the direction of travel on an implement drawn by a tractor. Each MSD chisel plow has a generally vertical shank made from heavy plate stock for mounting to the toolbar or frame of the implement and a plow point mounted at the bottom of the shank and intended to operate at the desired depth to fracture the soil at that depth and up to the surface. The soil is broken in a trough of increasing width progressing from the operating depth of the plow point to the surface of the soil. Not all the soil is tilled. Obviously, since the soil worked by the plows is fractured and loosened, it becomes aerated or "puffed up"; and each MSD chisel plow leaves behind it a slightly elevated profile of loosened soil relative to the compacted soil which is not tilled by the row unit.
In loosening and fracturing soil, an MSD chisel plow, thus, necessarily creates a slight berm or ridge of raised, loosened soil after working the soil. The height of the berm may be more pronounced with little or no lateral displacement of the soil and surface residue during plowing. If plowing is done in the fall, then the loosened soil tends to compact with time and the effects of weather, and the shape of the soil after settling back over the winter may leave an uneven surface profile. If the berm is too high, soil may be displaced off the berm into the region between swaths worked by the row units, thus creating an undesirable lateral displacement of soil, and an even more uneven surface profile.
It is desirable to use plow points which fracture and loosen the soil, but which do not throw the soil laterally to the side of the chisel plow, such as is disclosed in U.S. Pat. No. 5,540,288, entitled "PRIMARY TILLAGE UNIT WITH REDUCED DISTURBANCE OF SURFACE SOIL AND RESIDUE". If the soil is displaced from the trough or swath in which the row unit operates, then, after the loosened soil becomes compacted over time, there will be a net lateral displacement of soil, and a slight swale or trough will be created where the chisel plows had operated, after the loosened soil re-compacts with time and weathering. This effect can be cumulative over the years for those cases, which are believed to be significant in number, where the farmer plants row crops in the same row locations, year after year.
Moreover, there has been a desire to employ chisel plows with narrow, generally vertical shanks, formed from flat stock, such as disclosed in the '288 patent. These shanks are more rigid and more narrow than the curved shanks of parabolic shank chisel plows, which are designed to lift and "boil" the soil during operation, creating substantial soil and residue displacement. The shank is obviously a necessary element for mounting the breaking point, but it otherwise has no soil-tilling function, and it leaves behind it a furrow, the width of which depends on the width of the shank, the design of the leading edge of the shank, and to some extent, the soil-lifting and fracturing action of the point.
The furrow left by the shank behind a chisel plow does not have a substantial effect with respect to soil erosion, but it is considered to be undesirable for those farmers (and their numbers are growing) who desire to plow in the fall, after harvest, and then do no further tillage prior to planting the following spring.